We obtained TiNiSn-based half-Heusler HfxTi1−xNiSn0.97Sb0.03 bulks with 85%–96% relative densities via 5-min microwave synthesis and 20-min microwave sintering in sealed vacuum. The phase composition and microstructure of samples were characterized by X-ray diffractometer (XRD) and scanning electron microscopy (SEM). Thermoelectric (TE) properties were measured, i.e., Seebeck coefficient (S), electrical resistivity (ρ), and thermal conductivity (κ) through Seebeck coefficient/resistance analysis system (S/RAs) and laser flash thermal analyzer (LFT). The results show that the nearly single phase exists after microwave sintering. The grain sizes and the number of grain boundaries decrease with increase in Hf-doping amount due to an increase in point defects. The matrix grains for Hf0.1Ti0.9NiSn0.97Sb0.03 are ~ 10 μm. The nanoscle pores and precipitates are present as second phases in matrix grain. The real composition for Hf0.1Ti0.9NiSn0.97Sb0.03 matrix grain is Hf3.51Ti28.76Ni34.76Sn31.55Sb1.43. The variation trends of electrical resistivity, Seebeck coefficient, power factor, and thermal conductivity were analyzed in detail. The maximum figure of merit (ZT) of 0.46 is obtained for Hf0.1Ti0.9NiSnSn0.97Sb0.03 at 723 K. The innovation route exhibits advantages for predation of TE bulks when compared to the conventional methods, especially in terms of efficiency while it still maintains TE performance. © 2019, The Nonferrous Metals Society of China and Springer-Verlag GmbH Germany, part of Springer Nature.

The preparation of half-Heusler thermoelectric bulk is complex and time-consuming. In the present work, Sb doped TiNiSbxSn1-x bulks (x=0.01, 0.02, 0.03 and 0.04) were prepared via cold press forming, microwave synthesis and sintering in vacuumed sealed quartz in a few minutes. The microstructures of samples were characterized by using X-ray diffractometer (XRD) and scanning electron microscopy (SEM) techniques. The thermoelectric properties i.e. Seebeck coefficient (S), electrical resistivity (ρ) and thermal conductivity (κ) were measured on Seebeck coefficient/resistance analysis system (S/RAs) and laser flash thermal analyzer (LFT). The results show that high purity single phase was obtained after microwave sintering. The point defects came from Sb doping and the in-suit nanostructures attributed to microwave sintering process were found to lead to special microstructure. The variation trends of S, ρ, κ with temperature were analyzed. The influences of Sb doping to electrical and thermal properties were discussed. The electrical resistivity was decreased by ~84% at the cost of decreasing the Seebeck coefficient by ~25-30%. The maximum power factor of 2560 μWm-1K-2 was achieved at 673K. The lattice and total thermal conductivities are merely 1.1-1.3 and 3.8-4.0 Wm-1K-1 respectively. The thermoelectric figure of merit for TiNiSb0.03Sn0.97 was enhanced from 0.30 (773K) to 0.44 (673K and 723K) when compared to that of non-doped TiNiSn. © 2017 Elsevier Ltd and Techna Group S.r.l.

The half-Fleusler thermoelectric bulks ZrxTi1-xNiSn (x = 0.1, 0.2, 0.3, 0.4) were rapidly prepared by microwave heating. The phase composition and microstructure were characterized by X-ray diffractometer (XRD) and scanning electron microscopy (SEM). The electrical and thermal properties were measured by Seebeck coefficient/resistance analysis system (S/RAs) and laser flash thermal analyzer (LFT). The point defects came from Zr-substitution and the in-situ nanostructure attributed to microwave sintering were found to lead to special microstructure and excellent thermal performance. The grain size of Zr0.3Ti0.7NiSn is similar to 10 mu m. The in-situ nanoscale pores and inclusions are about 300-500 nm. The highest ZT 0.60 for Zr0.3Ti0.7NiSn was achieved at 673 K.